A sexual act which one participant presses their anus against their parther's anus and poops a log directly into their partner's open anus. The turd moves like a submarine from one body into another.
I met a sailer named Pat. After topping him he who gave me a huge San FranciscoSubmarine. It was long, hard, and full of sea men.
When a man warms white wine in his mouth and spits it into a woman's rectum. As the wine loosens the fecal matter, the man ejaculates inside the woman's butt. The backdoor is complete when the woman returns the wine into the man's mouth.
This is the same as a Turkish Backdoor, but with wine. Proponents of the San Francisco version claim the wine loosens more fecal matter than the Turkish version with water.